This invention relates to a structure of a magnetoresistance (MR) sensor overlaid with a longitudinal biasing (LB) stack in a read region and the fabrication method of this structure and, more particularly, to the transverse and longitudinal pinning layers used in the MR sensor and the LB stack, respectively.
A magnetoresistance (MR) sensor is used in a read/write head to read magnetic fields on a recording medium of a magnetic storage device. An example is the read/write head of a computer hard disk or a magnetic recording tape. The read/write head is positioned closely adjacent to the recording medium, separated from the recording medium by an air bearing surface (ABS) that does not allow them to touch. A data bit is written onto an area of the recording medium using the writing portion of the read/write head by locally changing its magnetic state. That magnetic state is later sensed by the MR sensor to read the data bit.
Two known types of MR sensors are a giant magnetoresistance (GMR) sensor and a tunnel magnetoresistance (TMR) sensor. The general technical basis, construction, and operation of the GMR sensor are described, for example, in U.S. Pat. No. 5,436,778. The general technical basis, construction, and operation of the TMR sensor are described, for example, in U.S. Pat. No. 5,729,410. The disclosures of both patents are incorporated by reference in their entireties. These patents also describe the read/write heads and the magnetic storage systems.
The structure of the MR sensors, such as the GMR sensor or TMR sensor, includes two thin-film stacks separated by an intermediate nonmagnetic film used as a spacer layer. FIG. 1 illustrates one form of a conventional MR sensor, with a Cuxe2x80x94O spacer layer separating the two thin-film stacks. The first thin-film stack, referred to as the transverse biasing (TB) stack, includes layers above the seed layers and below the Cuxe2x80x94O spacer layer (FIG. 1). In this TB stack, two magnetizations (M2 and M3) are separated by a ruthenium (Ru) spacer layer, and are rigidly pinned by a transverse pinning layer in two directions lying the plane of the MR sensor and perpendicular to the ABS. The second thin-film stack, referred to as the sensing stack, includes layers above the Cuxe2x80x94O layer and below a cap layer (FIG. 1). In this sensing stack, the magnetization is biased in a longitudinal direction lying in the plane of the MR sensor and parallel to the ABS.
A transverse pinning layer and a longitudinal biasing structure are provided to maintain the mutually perpendicular orientations of these magnetizations. The transverse pinning layer, the Ptxe2x80x94Mn film in FIG. 1, is positioned adjacent to the lower ferromagnetic film in the transverse biasing stack. (The lower ferromagnetic film is referred to as a keeper layer, whose magnetization M3 partially cancels the magnetization M2 of the upper ferromagnetic film, which is referred to as the reference layer.) The longitudinal biasing structure may be positioned either at two edges of the MR sensor as in FIG. 2, or adjacent to the sensing stack only in two side regions as in FIG. 3, thereby longitudinally biasing the sensing stack in the read region for sensor stability. The transverse pinning layer is typically made of an antiferromagnetic (AFM) film, while the longitudinal biasing structure is typically made of either a hard magnetic (HM) film with a suitable seed layer for the MR sensor structure as shown in FIG. 2, or another antiferromagnetic film for the MR sensor structure as shown in FIG. 3.
The use of the hard magnetic film as the longitudinal biasing structure causes a reduction in the available sensing area due to magnetic stiffness at the two edges of the MR sensor, thereby decreasing the read efficiency. These edge effects are a major problem as the MR sensor is made smaller. In addition, the required magnetic moment of the hard magnetic film is typically more than six times that of the sensing stack, resulting in low signal sensitivity of the MR sensor. On the other hand, the use of another antiferromagnetic film as the longitudinal biasing structure leads to concerns regarding the feasibility of maintaining the mutually perpendicular magnetization orientations and regarding corrosion resistance.
As magnetic storage devices are developed with increasing densities of stored data and relative speeds of movement of the recording media, their operating temperatures are increased as well. The required operating temperatures of the MR sensors are now in excess of about 180xc2x0 C., and may be expected to rise even further. There is a need for a pinning approach that rigidly pins the magnetizations at these elevated temperatures as well as at lower temperatures, and also exhibits acceptable corrosion resistance. The present invention fulfills this need, and further provides related advantages.
The present invention provides a magnetoresistance (MR) sensor structure useful to read magnetic fields, and a fabrication method for this MR sensor structure. In the MR sensor, transverse and longitudinal pinning layers are made of an antiferromagnetic material, preferably Ptxe2x80x94Mn. The MR sensor structure is stable at high operating temperatures and has good corrosion resistance. Good flux closure is formed between the sensing stack and the longitudinal biasing stack. The required magnetic moment of the longitudinal biasing stack generally matches that of the sensing stack, resulting in high signal sensitivity of the sensor. The present approach may be used for different types of MR sensor structures, such as a giant magnetoresistance sensor and a tunnel magnetoresistance sensor.
In accordance with the invention, a magnetoresistance sensor structure comprises a magnetoresistance sensor having a sensor surface plane, a transverse direction lying in the sensor surface plane, and a longitudinal direction lying perpendicular to the transverse direction and in the sensor surface plane. The magnetoresistance sensor comprises a transverse biasing stack comprising a transverse pinning layer made of a transverse-pinning-layer antiferromagnetic material, and a transverse pinned layer structure overlying the transverse pinning layer. The magnetoresistance sensor further comprises a spacer layer overlying the transverse pinned layer structure, a sensing stack overlying the spacer layer, and a decoupling layer overlying the sensing stack. A longitudinal biasing stack overlies the magnetoresistance sensor. The longitudinal biasing stack comprises a longitudinal pinned layer and a longitudinal pinning layer overlying the longitudinal pinned layer and made of a longitudinal-pinning-layer antiferromagnetic material. Preferably, there is also a seed layer upon which the transverse biasing stack is deposited, and a cap layer overlying the longitudinal biasing stack.
The transverse pinned layer structure is rigidly pinned magnetically in the transverse direction by the transverse pinning layer at temperatures of from room temperature to at least 180xc2x0 C., and the longitudinal pinned layer is rigidly pinned magnetically in the longitudinal direction by the longitudinal pinning layer at temperatures of from room temperature to at least 180xc2x0 C. The magnetoresistance sensor may be of any operable type, such as a giant magnetoresistance sensor or a tunnel magnetoresistance sensor.
The transverse-pinning-layer antiferromagnetic material is preferably selected from the group consisting of Ptxe2x80x94Mn and Nixe2x80x94Mn, and the longitudinal-pinning-layer antiferromagnetic material is selected from the group consisting of Ptxe2x80x94Mn and Nixe2x80x94Mn. The transverse-pinning-layer antiferromagnetic material and the longitudinal-pinning-layer antiferromagnetic material may be the same material, and are most preferably both Ptxe2x80x94Mn.
A method for fabricating a magnetoresistance sensor structure comprises the step of forming a magnetoresistance sensor having a sensor surface plane, a transverse direction lying in the sensor surface plane, and a longitudinal direction lying perpendicular to the transverse direction and in the sensor surface plane. The step of forming the magnetoresistance sensor comprises the steps of depositing a transverse biasing stack comprising a transverse pinning layer made of a transverse-pinning-layer antiferromagnetic material, and a transverse pinned layer structure overlying the transverse pinning layer, depositing a spacer layer overlying the transverse pinned layer structure, depositing a sensing stack overlying the spacer layer, and depositing a decoupling layer overlying the sensing stack. Thereafter the magnetoresistance sensor is first annealed at a first annealing temperature and in a transverse first applied magnetic field to develop antiferromagnetism in the transverse pinning layer and to rigidly pin a magnetization of the transverse pinned layer in the transverse direction. A longitudinal biasing stack is thereafter formed overlying the magnetoresistance sensor. The step of forming the longitudinal biasing stack comprises the steps of depositing a longitudinal pinned layer, and depositing a longitudinal pinning layer overlying the longitudinal pinned layer and made of a longitudinal-pinning-layer antiferromagnetic material. Thereafter, the magnetoresistance sensor and the longitudinal biasing stack are second annealed at a second annealing temperature and in a longitudinal second applied magnetic field, to develop antiferromagnetism in the longitudinal pinning layer and to pin a magnetization of the longitudinal pinned layer in the longitudinal direction. The step of second annealing does not disrupt the magnetization of the transverse pinned layer structure.
In this method, the first annealing temperature is preferably from about 240xc2x0 C. to about 280xc2x0 C. and the transverse first applied magnetic field is from about 7.5 kOe to about 15 kOe. The second annealing temperature is preferably from about 220xc2x0 C. to about 260xc2x0 C. and the longitudinal second applied magnetic field is from about 10 Oe to about 1000 Oe.